fix(db): stop startup crash from MySQL composite-index key length

Prod was hard-down: InitializeJobTrackerAsync threw an unhandled
MySqlException ("Specified key was too long; max key length is 3072
bytes") while creating IX_JobApplications_OwnerUserId_FollowUpAt,
which crashed Program.Main before the app could start (surfaced to
users as a 500 on Google sign-in, but really affected every request).

Root cause: this reconciler assumes OwnerUserId is varchar(255), but
the live column was provisioned wider by an earlier EF migration,
close enough to the utf8mb4 3072-byte limit that pairing it with a
second column tips a composite index over.

Fix:
- Prefix-index OwnerUserId at 191 chars (safe under the legacy
  767-byte-per-column limit, still far wider than the GUID-like
  Identity ids actually stored) in every composite/unique index that
  includes it, so index creation no longer depends on the column's
  actual declared width.
- Wrap each CREATE INDEX in try/catch + LogWarning instead of letting
  it propagate: a schema reconciler is best-effort and one failed
  index must never crash startup, matching the existing non-fatal
  pattern already used a few lines below for legacy-schema ownership
  claims.

Backend build + full test suite (177 passing) verified green.

JobTrackerApi/Services/StartupInitializationExtensions.cs

@@ -977,105 +977,61 @@ public static class StartupInitializationExtensions
                         cmd.ExecuteNonQuery();
                     }
 
-                    if (!MySqlIndexExists(conn, "Companies", "IX_Companies_OwnerUserId"))
+                    // Schema reconciliation must never crash app startup: an index that fails
+                    // (e.g. combined key exceeds MySQL's 3072-byte limit because an older
+                    // migration made OwnerUserId wider than the varchar(255) this reconciler
+                    // assumes) is logged and skipped rather than taking prod down. OwnerUserId
+                    // is prefix-indexed at 191 chars (safe under utf8mb4's 767-byte legacy
+                    // per-column key limit, and far longer than the GUID-like Identity ids
+                    // actually stored there) so composite indexes stay well under the cap
+                    // regardless of the column's declared width.
+                    void TryCreateIndex(string table, string indexName, string columnsSql)
                     {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_Companies_OwnerUserId` ON `Companies` (`OwnerUserId`);";
-                        cmd.ExecuteNonQuery();
+                        if (MySqlIndexExists(conn, table, indexName)) return;
+                        try
+                        {
+                            using var cmd = conn.CreateCommand();
+                            cmd.CommandText = $"CREATE INDEX `{indexName}` ON `{table}` ({columnsSql});";
+                            cmd.ExecuteNonQuery();
+                        }
+                        catch (Exception ex)
+                        {
+                            app.Logger.LogWarning(ex, "Skipping index {Index} on {Table} during startup reconciliation.", indexName, table);
+                        }
                     }
 
-                    if (!MySqlIndexExists(conn, "JobApplications", "IX_JobApplications_OwnerUserId"))
+                    void TryCreateUniqueIndex(string table, string indexName, string columnsSql)
                     {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_JobApplications_OwnerUserId` ON `JobApplications` (`OwnerUserId`);";
-                        cmd.ExecuteNonQuery();
+                        if (MySqlIndexExists(conn, table, indexName)) return;
+                        try
+                        {
+                            using var cmd = conn.CreateCommand();
+                            cmd.CommandText = $"CREATE UNIQUE INDEX `{indexName}` ON `{table}` ({columnsSql});";
+                            cmd.ExecuteNonQuery();
+                        }
+                        catch (Exception ex)
+                        {
+                            app.Logger.LogWarning(ex, "Skipping unique index {Index} on {Table} during startup reconciliation.", indexName, table);
+                        }
                     }
 
+                    TryCreateIndex("Companies", "IX_Companies_OwnerUserId", "`OwnerUserId`(191)");
+                    TryCreateIndex("JobApplications", "IX_JobApplications_OwnerUserId", "`OwnerUserId`(191)");
+
                     // Hot-path composite indexes for tenant-scoped list/board/stats/analytics
                     // (OwnerUserId + IsDeleted) and reminders (OwnerUserId + FollowUpAt).
-                    if (!MySqlIndexExists(conn, "JobApplications", "IX_JobApplications_OwnerUserId_IsDeleted"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_JobApplications_OwnerUserId_IsDeleted` ON `JobApplications` (`OwnerUserId`, `IsDeleted`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "JobApplications", "IX_JobApplications_OwnerUserId_FollowUpAt"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_JobApplications_OwnerUserId_FollowUpAt` ON `JobApplications` (`OwnerUserId`, `FollowUpAt`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "CvUploadArtifacts", "IX_CvUploadArtifacts_OwnerUserId_UploadedAtUtc"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_CvUploadArtifacts_OwnerUserId_UploadedAtUtc` ON `CvUploadArtifacts` (`OwnerUserId`, `UploadedAtUtc`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "CvExtractionRuns", "IX_CvExtractionRuns_OwnerUserId_StartedAtUtc"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_CvExtractionRuns_OwnerUserId_StartedAtUtc` ON `CvExtractionRuns` (`OwnerUserId`, `StartedAtUtc`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "CvExtractionRuns", "IX_CvExtractionRuns_ArtifactId"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_CvExtractionRuns_ArtifactId` ON `CvExtractionRuns` (`ArtifactId`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "GmailConnections", "IX_GmailConnections_OwnerUserId"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_GmailConnections_OwnerUserId` ON `GmailConnections` (`OwnerUserId`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "GmailConnections", "IX_GmailConnections_OwnerUserId_GmailAddress"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE UNIQUE INDEX `IX_GmailConnections_OwnerUserId_GmailAddress` ON `GmailConnections` (`OwnerUserId`, `GmailAddress`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "MicrosoftGraphConnections", "IX_MicrosoftGraphConnections_OwnerUserId"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_MicrosoftGraphConnections_OwnerUserId` ON `MicrosoftGraphConnections` (`OwnerUserId`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "MicrosoftGraphConnections", "IX_MicrosoftGraphConnections_OwnerUserId_MailAddress"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE UNIQUE INDEX `IX_MicrosoftGraphConnections_OwnerUserId_MailAddress` ON `MicrosoftGraphConnections` (`OwnerUserId`, `MailAddress`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "ImapConnections", "IX_ImapConnections_OwnerUserId"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE UNIQUE INDEX `IX_ImapConnections_OwnerUserId` ON `ImapConnections` (`OwnerUserId`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "TailoredCvDrafts", "IX_TailoredCvDrafts_OwnerUserId_JobApplicationId"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE UNIQUE INDEX `IX_TailoredCvDrafts_OwnerUserId_JobApplicationId` ON `TailoredCvDrafts` (`OwnerUserId`, `JobApplicationId`);";
-                        cmd.ExecuteNonQuery();
-                    }
-
-                    if (!MySqlIndexExists(conn, "TailoredCvDrafts", "IX_TailoredCvDrafts_JobApplicationId"))
-                    {
-                        using var cmd = conn.CreateCommand();
-                        cmd.CommandText = "CREATE INDEX `IX_TailoredCvDrafts_JobApplicationId` ON `TailoredCvDrafts` (`JobApplicationId`);";
-                        cmd.ExecuteNonQuery();
-                    }
+                    TryCreateIndex("JobApplications", "IX_JobApplications_OwnerUserId_IsDeleted", "`OwnerUserId`(191), `IsDeleted`");
+                    TryCreateIndex("JobApplications", "IX_JobApplications_OwnerUserId_FollowUpAt", "`OwnerUserId`(191), `FollowUpAt`");
+                    TryCreateIndex("CvUploadArtifacts", "IX_CvUploadArtifacts_OwnerUserId_UploadedAtUtc", "`OwnerUserId`(191), `UploadedAtUtc`");
+                    TryCreateIndex("CvExtractionRuns", "IX_CvExtractionRuns_OwnerUserId_StartedAtUtc", "`OwnerUserId`(191), `StartedAtUtc`");
+                    TryCreateIndex("CvExtractionRuns", "IX_CvExtractionRuns_ArtifactId", "`ArtifactId`");
+                    TryCreateIndex("GmailConnections", "IX_GmailConnections_OwnerUserId", "`OwnerUserId`(191)");
+                    TryCreateUniqueIndex("GmailConnections", "IX_GmailConnections_OwnerUserId_GmailAddress", "`OwnerUserId`(191), `GmailAddress`(191)");
+                    TryCreateIndex("MicrosoftGraphConnections", "IX_MicrosoftGraphConnections_OwnerUserId", "`OwnerUserId`(191)");
+                    TryCreateUniqueIndex("MicrosoftGraphConnections", "IX_MicrosoftGraphConnections_OwnerUserId_MailAddress", "`OwnerUserId`(191), `MailAddress`(191)");
+                    TryCreateUniqueIndex("ImapConnections", "IX_ImapConnections_OwnerUserId", "`OwnerUserId`(191)");
+                    TryCreateUniqueIndex("TailoredCvDrafts", "IX_TailoredCvDrafts_OwnerUserId_JobApplicationId", "`OwnerUserId`(191), `JobApplicationId`");
+                    TryCreateIndex("TailoredCvDrafts", "IX_TailoredCvDrafts_JobApplicationId", "`JobApplicationId`");
                 }
             }